In recent years, video input apparatuses such as digital cameras and the like which digitize captured image information and record that information as digital data on a recording medium and the like have prevailed in place of conventional silver halide photos and 8-mm films. With these apparatuses, captured image information itself can be transferred to an information processing apparatus represented by a personal computer, and can be displayed. By communicating such image data using a communication line, the image data can be instantaneously transmitted anywhere in the world. Paying attention to the convenience and easy transfer of such information, insurance companies that deal with evidence photos in accident processes, and construction companies that deal with records of the progress of building sites are considering use of digital image data.
Such digital data has the following three requirements.
The first requirement concerns confirmation of the originality of the digital image data. Since digital image data is easy to alter using an application program such as a commercially available photo retouch tool or the like, the reliability of digital data is lower than the conventional silver halide photos, and its evidentiary weight is poor. Hence, it is required to verify whether or not the captured digital image data has been altered.
The second requirement concerns confirmation of the edit record for the digital image data. A digital image has a requirement which conflicts with the first requirement that the digital image is not to be altered, as described above; it is sometimes desired to allow editing to some extent. In this case, the edit process itself for the digital image data is permitted, but it is required to confirm the contents of the applied edit process later.
The third requirement concerns holding of the edited digital image data. As a method of holding image data, a method of holding original image data in place of the edited image data itself has been proposed. With this method, original image data is held by appending information (image processing parameters and the like) associated with the applied edit process to that data. However, in the case of the method of holding the original image data, for example, even when a reduction process is applied to image data as the edit process, the data size itself cannot be reduced, and handling of image data may be consequently impaired. Upon browsing the edited image data, an image process must be executed based on the information associated with the (applied) edit process before display, and it is not always efficient. Hence, it is required to hold the edited image data itself in place of the original image data.
As a method that meets the first and second requirements, a method disclosed in a reference: Japanese Patent Laid-Open No. 2004-180278 has been proposed. According to this reference, edit record information is appended to original image data, and a digital signature is also appended to the appended edit record information, thus meeting the first and second requirements.
However, the method described in the above reference cannot meet the aforementioned third requirement. Even if the method described in the reference is modified to hold edited image data in place of original image data so as to meet the third requirement, the originality of the original image data cannot be verified. That is, the first requirement cannot be met in turn.